Control system for split coil heaters



July 18, 1950 P. P. BRIGGS ET AL coNTRoL SYSTEM FOR SPLIT con. HEATERS Filed aan. 2, 1948 1N V EN TOR.

P. P. emacs R. E. u oEBEcK BY Arron/vers IUPK OP Patented July 18, 1950 UNITED STATES PATENT ,OFFICE CONTROL SYSTEM FOR SPLIT COIL HEATERS Preston P. Briggs and Robert E. Loebeck, Bartlesville, Okl

a., asslgnors to Phillips Petroleum This invention relates to an automatic control system for split coil heaters. In one of its more specic aspects it relates to a method and apparatus for controlling a split coil operation wherein it is desired to fire all burners of a heater from one control and where the charge stock to the heater is taken directly from a process step and without the use of a surge storage.

One object of our invention is to provide a method for automatically operating a split coil heater assembly.

Another object of our invention is to provide an apparatus and a method for operating this apparatus wherein stock to be heated may be taken directly from a process step without the intermediate use of a surge vessel and heated directly in a split coil heater.

Still another object of our invention is to provide a process wherein parallel coils of a split coil heater are operated in such a manner as to maintain the heater effluent at a constant temperature regardless of the volumes of charge stock passed through the respective heating coils.

Still other objects and advantages will be appreciated by those skilled in the art upon reading the following specification which taken with the attached drawing respectively describes and illustrates a preferred embodiment of our invention.

Figure 1 illustrates diagrammatically one form of apparatus in which the process of our invention may be carried out. Figure 2 illustrates diagrammatically one form of our variable ratio controller assembly.

On reference to the drawing a process vessel sich as a fractionating column I is equipped with a liquid level controller assembler 4. From the bottom of the vessel I a pipe II) leads to a charge pump I I which pump discharges liquid in process through a pipe I2 to pipes I3 and I4. Pipe I4 is connected with the inlet end of coil No. 1 of a split coil heating assembly. Coil No. 1 is identified by reference numeral 2. The pipe I3 is connected with the inlet end of No. 2 heater coil identied by reference numeral 3. The outlet end of coll 2 is'connected with a pipe 2l which pipe joins the outlet end of coil 3 and both coils discharge into a pipe 28. Material passing through pipe 28 passes to a subsequent process step, or such other disposal as desired, not shown.

A liquid or gaseous fuel from a source, not shown, flows through a fuel line 20. through a pipe 23 and thence to one or more burners 23A disposed at convenient locations in the fire box of the heater. The pipe I4 is equipped with a motor valve Il which valve actually serves as a connecting link between the pipe I4 and the inlet end of the heater coil 2. The pipe I3 is also equipped with a motor valve I8 which serves as a connecting link between the end of pipe I3 and the inlet end of the heating coil 3. Pipe I4 carries an oriflce member I5 and pipe I3 carries a similar orifice member I6. These two orifice mem-bers or assemblies I5 and I8 are connected to the two sides of a recording ratio controller assembly 6 by means of two pairs of differential pressure tube assemblies 32 and 34, respectively. A tube 42 adapted to carry air under pressure connects one side of this recording ratio controller 6 with the motor of the motor valve it and tube, 25, connects the recording ratio controller 6 with a recording temperature controller assembly l. This latter assembly 1 is further connected electrically to a thermocouple I9 inserted in the outlet end of the heater coil 3 at the point indicated. 'Ihe orifice assembly I5 is also connected by another tube assembly 45 to a recording flow controller 5. The control point adjustment of controller 5 is connected by a tube 24 adapted for communication of air pressure from the liquid level controller assembly 4. A third tube 46 connects the recording flow controller 5 to the motor of the motor valve The iuel line 20 carries an orifice assembly 2| which is connected by a differential pressure tube assembly 4l to a recording ow controller 9. This flow controller 9 is connected pneumatically to the motor of the motor valve 22. The valve 22 serves as the connecting link between the fuel inlet pipe 20 and the pipe 23. The third connection from the recording flow controller 9 is connected by connection assembly 26 with one side of the recording temperature controller 8, the opposite side of which is connected electrically with a thermocouple in the pipe 28 at a point indicated by reference numeral 28A.

In the operation of this apparatus liquid bottoms accumulating in the bottom of the fractionator vessel I are transferred through pipe I0 under the influence of pump I I and discharged therefrom through pipe I2. One portion of this liquid charge material passes through pipe I4, orice I5 and motor valve I1 into and through the coil 2 and discharges therefrom through pipe 21. The remaining portion of the charge fluid passes through pipe I3, orifice I6, motor valve I8 and through heater coil 3 and from this coil heated liquid joins the liquid heated in coil 2 and the combined stream flows through pipe 28 to another process step, not shown. Liquid level controllers, as controller 4, are standard equipment and their operation is well known by those skilled in the art. The recording ow controller assembly 5 in conjunction with the motor valve I'I is also standard equipment, the operation of which is known. In the operation of two coil heater assemblies conventional practice is for the use o! a recording ratio controller for splitting the charge stream into two streams which are heated in the two coils of the heater. Such ratio controllers are manually set to control dividing of the charge stock stream into two streams and these streams bear a deilnite and fixed ratio of volumes to each other. For some operations, such controllers are usually set 1 to 1 or to some other definite or fixed ratio, so that streams of desired volumes will pass through the two coils of the heater.

We have found that in the operation of such a split coil heating system that conditions often arise in which it is desired to change frequently the ratio setting so that varying volumes, of charge stock will pass through the several heating coils in order to operate more efficiently split coil systems. For use in such systems we have devised the herein disclosed method of operation. A conventional recording ratio controller is equipped with pen arms one of which is manually set to control the flow of uid through one motor valve at a desired ratio to the volume of fluid passing through another motor valve. Our invention consists in adapting this manually operable ratio controller to vary automatically the ratio of the two streams of fluid.

Our invention also consists in providing a control arrangement for automatically controlling the flow through each coil of a two-coil heater by means of a ratio controller whereby the furnace eilluent temperature is maintained constant with the charge being fed directly from a preceding process step.

In order to control automatically this volume ratio setting of the controller 6 we install a thermocouple at point I 9 in the discharge of the heater coil 3 and connect this thermocouple electrically to temperature controller 'I and this controller 'I as mentioned before is connected by tube 25 to the ratio controller member of the recording controller 6. The operation of this apparatus is such that as the temperature of the fluid leaving the coil 3 rises or decreases the recording temperature controller 1 operates to change automatically the ratio of the volumes of the fluid stock passing` through the coils 3 and 2 by changing the ratio setting which in turn causes the ratio controller to operate the motor valve I8 to open somewhat or to close somewhat to adjust the flow of fluid to be heated. Under all conditions some liuuid from the bottom of the fractionator I flows through pipes I0, I2 and I4 and through motor valve I1 into the coil 2. The flow of fluid through coil 2 passes through the oriilce I5 and this flow is then recorded by the recording flow controller 5 as a matter of permanent record. The recording ratio controller Ii also records this same flow of fluid through oriilce I5 and based on this flow of fluid through oriilce I5 this controller 6 proportions the fluid passing into the coil 3 by operation of the motor valve I8. If, for some reason, the heating coil 3 cokes up somewhat and the transmission of heat from the fire box to the fluid being heated is less than normal the temperature of the fluid passing the thermocouple I9 will be too low and the recording temperature controller 1 will then operate to decrease the ratio of volumes of fluid entering the heating coil 3 to that entering heating coil 2 by changing the ratio setting of the recording ratio controller l which in turn operates to close somewhat the motor valve I 9.

The ratioA oi' the volumes as herein discussed is the volume of fluid passing through coil 2 to the volume passing through coil 3.

When these operational steps take place the volume of fluid to be heated in coil 3 is decreased somewhat and at the decreased flow through heating coil 3 the temperature of the fluid issuing from this heating coil and passing the thermocouple I9 will be higher than before the iow adjustment is made. Ii the temperature of the fluid now passing the thermocouple I9 is that desired for desired operation of the setting apparatus as determined by the controlled setting of the controller no further operational change in the ratio controller 8 will occur and operation will continue as now described until something occurs to change the temperature at the thermocouple point I Q or at the thermocouple point 28A.

If the fluid passing thermocouple point I9 is at a desired temperature any changes in temperature at the thermocouple point 28A will then be caused by variation in operation o' the heating coil 2. When such a temperature change occurs at point 28A it will be obvious that such temperature change was occasioned by the total heater output and thi` thermocouple 28A then operates through the recording temperature controller E and the recording flow controller 9 to operate the motor valve 22 to partly close the fuel line to the flow of fuel to the burners. latter operation if the thermocouple 28A shows too high a temperature then motor valve 22 is adapteddo throttle the fuel to the bin'ners and accordingly the burner temperature drops to such an extent that the temperature at the thermocouple 28A will decrease and when this temperature decreases a desired amount then the motor valve 22 will remain in its position and permit the flow of that amount of fuel required to heat the entire split charge in the furnace to the desired temperature. The ratio of the volume of the charge fluid passing through heater coil 3 to the volume passing through the heater coil 2 may remain more or less fixed over long periods of time depending, of course, on whether otherconditions change which might affect the operation of either the heating coil 3 or the heating coil 2. The ratio of the volume of fluid charge going through coil 3 to the volume of fluid going through coil 2 may change whether the combined volume going through both coils changes or does not change, and, likewise, the total volume of charge going through both coils may change in response to the operation of the liquid level controller 4 without changing the ratio of charge going through the two coils. The ratio of the charge of fluid going through the two coils is independent of the operation of the liquid level controller 4.

Referring now to Figure 2 of the drawing which shows some detail of the ratio controller, tube assembly 32 from orifice I 5 assembly of Figure 1 is connected with mechanism, not shown, to a pen arm 33. Tube assembly 34 from oriilce IB of Figure 1 is connected with mechanism, not shown,

' to pen arm 35. 7 Thus the indicator or pen arm 33 indicates or records the volume of fluid flowing through the coil 2 while the indicator or pen arm 35 indicates or records the flow of fluid through the heater coil 3.

1| The tube 25 from the recording temperature In this controller 1 is connected with a bellows 31, which in turn is connected with the adjusting ratio linkage assembly 48. This assembly 48 is pivoted at point 44 with a ratio pointer 38, which is further pivoted at 43 in order to magnify the movement of the ratio pointer 38.

An arm 39 is the controlled flow controller arm, and when this arm is set at a definite flow by the ratio setting of the flow through coil 3 to the flow through coil 2, then air issuing from a bleed orifice 40 increases 0r decreases and air pressure in tube 42 decreases or increases and since tu-be 42 is connected with the motor of valve i8, this change of pressure causes a change of setting of the valve i8, which change of course alters the flow of fluid to be heated in coil 3. When this change in flow of fluid occurs as indicated by flow through the orifice I6, this flow is accordingly indicated or recorded by indicator or pen arm 35. This pen arm is adapted to follow the positioning of the controlled flow arm 39. For this last operation it is immaterial whether the ratio linkage 48 is set manually or automatically and weA have found that by use of the bellows 31 the operation of which is responsive to temperature in the outlet of coil 3, that the controlled flow controller arm 39 follows the ratio arm 3B.

This entire ratio control instrument 6 may be housed in a case 3i for protection.

Those skilled in the art will immediately appreciate that the system herein disclosed is capable of variation in its details without departure from the subject matter of the novel combination herein described. As an example, the motor valves il, I8 and 22 may be electrically operated, in place of pneumaticaily operated as herein described Without departing from the novel combination. Also, rotameters or any other rate of flow indicating device can be used in place of the differential device mentioned herein. I do not therefore desire to be strictly limited to the disclosure as set forth herein for illustration purposes but only as required by the appended claims.

We claim:

1. A method for operating a two-coil split coil assembly for heating a fluid comprising passing a portion of the fluid to be heated through one coil of said two-coil assembly, passing the remainder of the fluid to be heated through the second coil, controlling the rate of flow of fluid through said second coil in response to the rate of ow of fluid through said first coil, and controlling the ratio of the rate of flow of fluid in said second coil to the rate of flow of fluid in said first coil in response to the temperature of the fluid discharging from said second coil.

2. A method for operating a two-coil split coil assembly for heating a fluid comprising passing a portion of the fluid to be heated through one coil of said two-coil assembly and therein heating said fluid, passing the remainder of the uid to be heated through the second coil and therein heating the fluid passing therethrough, measuring the rate of flow of the portion of fluid passing through said one coil, controlling the rate of flow of fluid through the second coil in response to the rate of flow of fluid in said first coil, and controlling the ratio of the rate of flow of fluid in said second coil to the rate of ow of fluid in the first coil in response to the temperature of. the fluid discharging from said second coil.

3. A method for operating a two-coil split coil assembly for heating a fluid comprising withdrawing said fluid to be heated directly from' a process step and at a nonuniiorm rate, passing a portion of said withdrawn fluid to be heated through one coil of said two-coil assembly at a nonuniform rate and therein heating said portion of fluid by indirect heat exchange with burning fuel, passing the remainder oi' said withdrawn fluid to `be heated through the second coll and therein heating said remainder of the fluid by indirect heat exchange with said burning fuel, continuously measuring the rate of flow of the portion of fluid passing through said one coil at said nonuniform rate. controlling the rate of flow of fluid through the second coil at one instant of time in response to the rate of flow of fluid in said first coil at the same instant of time, and controlling the ratio oi.' the rate of flow of fluid in said second coil to the rate of flow oi fluid in the first coil in response to the temperature of the fluid discharging from said second coil.

4. An apparatus for controlling the heating oi' a. fluid in a two-coil split coil heating assembly, comprising, in combination, a process vessel, a first heating coil and a second heating coil in split coil arrangement and through which Huid to be heated is passed, manifold conduit means through which-fluid to be heated is passed from the process vessel to said coils, manifold conduit means into which efiluents from the two coils are combined into one stream, a furnace re box in which are disposed the two coils of said split coil assembly and a fuel burner, a conduit in fluid communication with said burner for passage of fluid fuel, a liquid level control means in operational communication with said process vessel, a motor valve responsive to said liquid level control means disposed in said rst coil and adapted to control flow of fluid through said first coil, a second motor valve disposed in said second heating coil, means responsive to the flow of fluid through said first coil for operating said second valve, said second motor valve adapted to control the flow of fluid through said second heating coil in proportion to the flow of fluid through said first coil, a temperature controller means in communication with the outlet end of said second heating coil and adapted to control the ratio of the volume of fluid flowing in the second coil to the Volume of the fluid flowing in the first coil by controlling the flow of fluid to the second coil, means for controlling the flow of fuel in said fuel conduit, said latter means adapted to operate in response to the temperature of the one stream of fluid passing through said outlet manifold conduit means.

5. In combination with the steps of claim 3, the additional steps of combining the streams of heated fluid issuing from the two coils and controlling the flow of said fuel to the heating assembly in response to the temperature of said combined stream.

' PRESTON P. BRIGGS.

ROBERT E. LOEBECK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,006,035 Stewart June 25, 1935 2,337,851 Junkins Dec. 28, 1943 Crtiicate of Correction Patent No. 2,515,490 July 18, 1950 PRESTON P. BRIGGS ET AL.

It is hereby certified that erro'i` appears in the printed specification of the above numbered patent requiring correctlon as follows:

Column 4, line 4, for coil 2 read coil 3; line 5, for coil 3, read coil 2' and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the case in the Patent Oflce.

Signed and sealed this 24th day of October, A. D. 1950.

THOMAS F. MURPHY,

Assistant Gommz'sszoner of Patents. 

